Control and supply system

ABSTRACT

The invention relates to a control and supply system for electrical devices, comprising at least one voltage supply and control device above sea level, a subsea cable connecting said voltage supply and control device with the electrical devices, and a control and actuating device which is associated essentially in situ with the electrical devices. The aim of the invention is to improve one such control and supply system in such a way that supplies are possible over larger distances, using fewer means, obtaining higher efficiency and making better use of the system. In order to achieve this, the voltage supply and control device comprises at least one AC/DC converter for producing a direct voltage in order to feed the subsea cable, the control and actuating device is associated with at least one DC/DC or DC/AC converter for converting the direct voltage transmitted by the sub-sea cable into a direct voltage or an alternating voltage, and the voltage generated thereby can be transmitted to the electrical device via the connecting line.

BACKGROUND OF THE INVENTION

The invention relates to a control and supply system for electricaldevices, comprising at least one voltage supply and control device abovesea level, a subsea cable connecting said voltage supply and controldevice with the electrical devices, and a control and actuating devicewhich is associated essentially in situ with the electrical devices.

Such control and supply systems are used, for example, in the productionof natural gas and mineral oil. In this respect, the application maytake place with terrestrial and maritime drilling wells.

With maritime wells one part of the control and supply system isarranged on a platform above the sea surface. This part is in particulara voltage supply and control device which is connected via a subseacable to the control and actuating device below the sea surface or alsoon the sea bed. The control and actuating device is connected to variouselectrical devices, such as motors, electrical actuators and similarequipment via appropriate connecting lines.

With this type of control and supply system known from practice,alternating voltage is transmitted through a subsea cable, whereby theamplitude and frequency of the alternating voltage is already selectedsuch that, for example, on the end of the cable associated with theelectrical devices a suitable supply voltage for the devices isprovided. For the direct control of each device a separate subsea cablecan be provided for each device. The data transmission also occurs viaseparate subsea cables.

A disadvantage with this known control and supply system is that, forexample, for a supply of an electrical device with 240 VAC and with anoriginal voltage feed of 600 VAC for the transmission of the appropriatepower to the electrical devices and, for example, a length of subseacable of 30 or 50 km, a cross-sectional area of 100 to 200 mm² is neededfor the cable. In addition, data lines are required, so that a subseacable with a substantial diameter arises.

In the above it has been assumed that 240 VAC is sufficient for theelectrical devices. However, it has now been found that higher voltagesare required, for example, in order to be able to actuate servomotors aselectrical devices with higher power, for example, to close valves inthe production of natural gas or mineral oil in a maximum time period ofone minute. With the application of such electrical devices suppliedwith a higher voltage the cross-sectional area of the subsea cable withthe known control and supply system would increase still further.

In addition, it has been found in practice that on starting a servomotoras an electrical device and in particular for servomotors with a higherpower, even with a slow starting process, a return signal occurs via thesubsea cable to the voltage supply and control device indicating thestarting process of the servomotor as a short circuit at the end of thecable. This leads to the switching off of a system automaticallyprotected against short circuit.

Furthermore, with the previously described control and supply system anefficiency for the overall system of only 27% is obtained referred tothe output power. With another control and supply system known frompractice, transmission of alternating voltage also occurs through thesubsea cable. However, with this system an alternating voltage, forexample, at 10,000 VAC is transmitted via the subsea cable and at thecontrol and actuating device it is reduced, for example, by atransformer to the voltage values required by the electrical devices. Inaddition, a number of power capacitors must be used to smooth thevoltage again after the reduction. In order to be able to reduce, whererequired, the conductor cross-sectional areas for the subsea cable withthis other known system, a power factor correction is also implementedto obtain an adequate efficiency for the overall system. Furtherdevices, which are very complex and expensive, are needed for thiscorrection. However, even with the complete expansion of the previouslymentioned system, the efficiency normally is less than 70% and thecross-sectional areas for a conductor in the subsea cable amount toabout 16 or 26 mm² for a length of 30, or respectively 50 km.

BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS

The object of the invention is to improve a control and supply system ofthe type mentioned at the beginning such that with less complexity,higher efficiency and better system usage, supply is possible overlarger distances.

This object is solved in relationship with the characteristics of thegeneric term of claim 1 such that the voltage supply and control devicefor the production of a direct voltage for feeding into the subsea cablecomprises at least one AC/DC converter, the control and actuating deviceis associated with at least one DC/DC or DC/AC converter for convertingthe direct voltage transmitted by the subsea cable into a direct voltageor alternating voltage and the voltage generated thereby can betransmitted to the electrical devices via the connecting lines. Thismeans that according to the invention direct voltage is transmitted viathe long subsea cables, whereby the conversion from alternating voltageinto direct voltage or vice versa from direct voltage into alternatingvoltage only takes place at the ends of the subsea cable. With directvoltage and the corresponding direct current, only real power istransmitted via the subsea cable and no apparent power. This means thatthe power factor is 1. Due to the direct voltage transmission along thesubsea cable, even with high voltages only slight losses are present incomparison to a transmission of alternating voltage with previouslyknown systems.

Furthermore, with the transmission of direct voltage only smallcross-sectional areas arise for a conductor in the subsea cable whichmay be only one tenth or less of the cross-sectional areas for thetransmission of alternating voltage.

Due to the DC/DC or DC/AC converter in the area of the control andactuating device, a corresponding conversion of the direct voltage takesplace into the required direct or alternating voltage values, such asfor example, 240 V or 300 V with the appropriate frequency, for theelectrical devices such as motors, actuators and similar equipment.

The system according to the invention is therefore distinguished by itssimplicity and higher efficiency (at least 70%), whereby a significantcost saving can be obtained solely by the significant reduction of thecross-sectional area of the conductors in the subsea cable.

A simple voltage source for the system, which can also normally be usedfor other applications, can be seen in that an alternating voltagesource is connected to the supply voltage and control device for thesupply with an especially three-phase alternating voltage source.

With the previously known systems it is also possible to transmit databetween the voltage supply and control device and the control andactuating device. Normally, a separate cable is used for this.

According to the invention, another advantage arises in that the directvoltage transmission along the subsea cable is free of any highfrequencies and therefore voltage frequencies directly corresponding tothe direct voltage can be modulated onto the direct voltage in a simplemanner for data transmission. This can especially take place in that thevoltage and control device and the control and actuation device eachexhibit at least one data modulation device.

An especially simple and effective type of data feed can be seen in thatthe data modulation device of the voltage supply and control device isarranged after the DC/DC or AC/DC converter.

A suitable input of information or data can occur directly in the areaof the data modulation device via appropriate input devices. However,there is also the possibility that a suitable data and signal feedoccurs from a more remote position. To achieve this, the voltage andcontrol device can be connected to an external data transmission device.The appropriate data can be transmitted through it to the datamodulation device or received from it.

In order to be able to receive or feed in data in a simple and analogousmanner also in the area of the control and actuation device, the datamodulation device of the control and actuation device can be positionedbefore the DC/DC or DC/AC converter.

In this way the data is fed in and also obtained from the directvoltage.

In order to prevent the occurrence of high currents and, whereapplicable, of damage to the relevant electrical devices, especially onthe sea bed, an overcurrent control device can be assigned to the DC/DCor DC/AC converter.

With a DC/DC converter on the sea bed the high direct voltage of anumber of thousands of volts fed from the surface of the sea is split upinto appropriate direct voltages for the supply of the individualdevices on the sea bed.

In order to be certain that the electrical devices are supplied withsuitable voltage values, the DC/AC converter can be inductively coupledwith an alternating voltage measurement device, especially with avoltage shunt regulator. Due to the voltage shunt regulator, the systemcan, for example, run under full voltage also before the actuation ofthe electrical devices, whereby the voltage shunt regulator takes overthe dynamic load regulation and then can reduce the voltage toappropriately low values.

Due to the inductive coupling, it is established as a furthercharacteristic of the invention that suitable plug connections or otherconnections between subsea cables and electrical devices are notoperated with direct voltage. It is generally known that even slightmoisture is hazardous for the transmission of direct voltage andespecially salt water acts as a galvanic element with direct voltage andwould very quickly damage metallic contact surfaces. In order to keepthe expense of such connections low, the inductive coupling takes placebelow sea level and the following passage of the voltage occurs throughalternating voltage for which the usual, known maritime electricalconnectors can be used.

By using the usual electrical connectors, it is also possible for allthe connected parts to be recovered and to be fetched from below sealevel and, for example, to service them and reuse them later. Accordingto the invention a fixed and non-releasable connection between, forexample, the subsea cable and appropriate devices is not required.

For the inductive coupling a transformer can be used, which, forexample, also directly carries out the conversion of the direct voltageinto the alternating voltage values for the electrical devices.

Such a transformer may comprise two separable, largely symmetrical andmutually associated coil half-cores.

In order to be able to simultaneously interchange data over the air gapbetween the coil half-cores, a data modulation device can be assigned toeach coil half-core for the transmission of data.

In order to control and monitor the conversion of the direct voltageinto alternating voltage and to control and monitor at least theappropriate data modulation devices of the coil half-cores, a couplingcontrol device appropriate to controlling the data modulation devices,the DC/AC converter and/or the alternating voltage measurement devicecan be assigned to each coil half-core. A return signal to the voltagesupply and control device for regulating the direct voltage can beprovided from the alternating voltage measurement device, whereby thereturn signal occurs via the appropriate coupling control devices, datamodulation devices for the coil half-cores, data modulation device ofthe control and actuating device, subsea cable and data modulationdevice of the voltage supply and control device. In this way acontinuous bidirectional data interchange between the voltage supply andcontrol device and the control and actuation device is possible.

With a simple embodiment without further control devices, thealternating voltage measurement device can be connected to theelectrical devices for their supply.

In order to measure the alternating voltage provided by the DC/ACconverter in a simple manner by the alternating voltage measurementdevice and to supply the electrical devices with suitable voltagevalues, the alternating voltage measurement device can in particularmeasure an amplitude of the alternating voltage.

In this connection, it is advantageous if the alternating voltagesupplied by the DC/AC converter is, for example, a rectangular wavevoltage. With this voltage the various electrical devices can besupplied with a stable voltage and sufficient power.

A separate voltage stabilization, for example, using a Zener diodearrangement is no longer necessary due to the alternating voltagemeasurement device with voltage shunt regulator according to theinvention, because the alternating voltage provided by this circuit isalready statically and dynamically stabilized.

For the transmission of the direct voltage and also the electricalsignals along the subsea cable, the cable can be advantageously formedfrom coaxial conductors. These exhibit optimum properties with regard toattenuation and immunity with regard to radiated noise and they enable ahigh data transmission rate of at least 100 to 600 kbaud. Furthermore,bidirectional transmission of data along the subsea cable can also becarried out simply.

The transformer can be realized such that the air gap between the twocoil half-cores is, for example, at the most 4 mm or especially at themost 2 mm. In addition, appropriate materials for the coil half-corescan be used which are not susceptible to attack by sea water, such asarrangements of corrosion-resistant transformer steel sheet or plasticencapsulated magnetic powder mixtures for the appropriate coil corematerials.

In order to be able to also pass data in the direction of the voltagesupply and control device directly from the electrical devices or thealternating voltage measurement device, the voltage shunt regulator canbe realized bidirectionally.

Due to the application according to the invention of direct voltage ordirect current and the resulting possible small cross-sectional areas ofthe conductors in the subsea cable, there is also the possibility thatfor each electrical device a separate connecting conductor can beprovided in the subsea cable. In this relationship it must be noted thatan electrical unit, for example, a single motor or a single actuator canalso be a suitable tree structure or group of electrical motors,actuators or other electrical devices.

A suitably simple coupling of data—also multi-channel—can be realized inthat the system exhibits a multiplexer device for data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following an advantageous embodiment of the invention isexplained in more detail based on the figures enclosed in the drawing.

The following are shown:

FIG. 1 a-c a schematic diagram of various control and supply systems asa comparison, whereby the control and supply system according to theinvention is illustrated in FIG. 1 c;

FIG. 2 a block diagram of the control and supply system according to theinvention as in FIG. 1 c.

FIG. 1 shows various control and supply systems of which those in FIGS.1(a) and (b) are known in practice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the control and supply system according to FIG. 1(a) a voltagesupply and control device 3 with appropriate voltage source andmultiplexer device 25 is arranged above the surface of the sea 4. Thevoltage supply occurs via alternating voltage, which is transmitteddirectly via a subsea cable 5 to a control and actuating device 6. Thisis arranged below sea level and is connected via connecting lines 26 toappropriate electrical devices 2 or electrical units 24. Such anelectrical unit 24 may be formed by a group of electrical devices 2,which, for example, are arranged in the form of a tree structure and arecontrolled and actuated on a common basis.

A data cable 27 is provided for the data transmission between thevoltage supply and control device 3 and the control and actuating device6. This is preferably composed of coaxial conductors.

Normally, an alternating voltage of a maximum of 600 VAC is transmittedalong the subsea cable 5. For the supply of the appropriate electricaldevices with 240 VAC and appropriate power, cross-sectional areas of atleast 175 mm² for appropriate conductors are required in the subseacable for, for example, a length of 50 km.

The control and actuation device 6 includes at least one motor actuationdevice 31 and a control system 32. The various motors as electricaldevices 2 can be used here for the actuation of valves, BOPs (blow-outpreventers) and similar equipment which is used for the production ofmineral oil or gas on the sea bed.

With the other known control and supply system according to FIG. 1(b)transmission of alternating voltage along the subsea cable 5 alsooccurs. In this case however a voltage of a maximum of 10,000 VAC istransmitted which is reduced before the control and actuation device 6by a suitable transformer 33 to the voltage values required for theelectrical devices. Also, with this known system a separate dataconductor 27 is provided as a coaxial cable or similar. The control andactuating device 6 according to FIG. 11(b) requires expensive powercapacitors 34 in order to smooth the reduced alternating voltageappropriately. In addition, with this system, as with the systemaccording to FIG. 1(a), power factor correction devices are needed tolower the apparent power of the system. Such correction devices arenormally quite expensive and consist of capacitors or similar.

With the system according to FIG. 1(b) and for appropriate voltagevalues and powers for the electrical devices on the sea bed, conductorcross-sectional areas in the subsea cable of, for example, at least 75mm² arise for a length of 50 km or with power factor correction at leasta cross-sectional area of 26 mm² for a 50 km length.

According to the invention and as in FIG. 1(c), alternating voltage isnot transmitted via the subsea cable 5, but instead direct voltage isused. The voltage supply and control device 3 exhibits at least oneAC/DC converter 7, which converts a suitable alternating voltage from analternating voltage source 9, see FIG. 2, into direct voltage. In thearea of the control and actuation device 6 a DC/DC or DC/AC converter 8is provided analogously for the conversion of the direct voltage intodirect or alternating voltage. Since, according to the invention, adirect voltage is transmitted through the subsea cable 5,correspondingly no transmission of high frequency voltages occurs, sothat signals for data transmission can be modulated onto the directvoltage in a simple manner. This takes place through the multiplexerdevice 25 and through an appropriate cable coupler 34. Demodulation ofthe data occurs appropriately in the area of the control and actuationdevice 6.

With the implementation of the converter 8 as DC/DC converter aconversion of the high direct voltage transmitted through the subseacable 5 occurs appropriately into the direct voltages required for thesupply of the appropriate device on the sea bed. In this connection itmust be noted that with a direct voltage supply of the device at the seasurface a suitable data interchange with this device is simplified,because appropriate data signals can be modulated onto the directvoltage signal in a simple manner.

In the following the control and supply system 1 according to FIG. 1(c)is described in more detail based on a block diagram in FIG. 2.

With the embodiment of the control and supply system 1 according to theinvention and as in FIG. 2, a voltage supply and control device 3 isarranged above the sea surface 4 and a control and actuation device 6below this sea surface 4. The link between these two is realized by asubsea cable 5.

The voltage supply and control device 3 comprises at least one AC/DCconverter 7 and a data modulation device 10. Furthermore, a surfacecontrol device 28, through which the control of the AC/DC converter 7and also of the data modulation device 10 occurs, is assigned to bothpreviously mentioned units.

The voltage supply and control device 3 is connected to an alternatingvoltage source 9 which provides a three-phase alternating voltage.Furthermore, the voltage supply and control device 3 is connected to adata transmission device 11 which can be positioned remote from thevoltage supply and control device 3, but which is still part of thecontrol and supply system 1. The control of the complete system and itsmonitoring can occur through the data transmission device 11.

The arrows shown between the various units in the system indicatethrough the arrow direction a transmission of voltage or data, wherebygenerally a bidirectional data transmission is possible.

The control and actuation device 6 is positioned below the sea surface 4and, for example, on the sea bed. It comprises a data modulation device12 for demodulation of the data transmitted through the subsea cable 5,but also for the modulation of appropriate data onto the voltagetransmitted through the subsea cable 5 when such data is transmitted inthe reverse direction from the control and actuation device 6 to thevoltage supply and control device 3.

Following the data modulation device 12, the control and actuationdevice 6 comprises a DC/AC converter 8. Using this, the direct voltagetransmitted through the subsea cable 5 is converted back into anappropriate alternating voltage. An overcurrent control device 13 isassigned to the DC/AC converter 8. Following conversion of the directvoltage into alternating voltage by the DC/AC converter 8, an inductivetransmission of the alternating voltage occurs to an alternating voltagemeasurement device 14. The inductive transmission occurs through atransformer 16 consisting of two coil half-cores 17, 18. An air gap 23is formed between these coil half-cores.

The alternating voltage measurement device 14 is especially used for thedetermination of amplitude values of the alternating voltage and avoltage shunt regulator 15 is assigned to the measurement device. Thisprovides an appropriate static and dynamic stabilization of thealternating voltage, whereby the voltage shunt regulator 15 isbidirectional and, together with the alternating voltage measurementdevice 14, is positioned on the output of the transformer 16. Then, thestabilized alternating voltage is passed to a subsea voltage source 30to which the various electrical devices 2 or units 24 are connected viaelectrical connecting lines 26.

A data modulation device 19, 20 as well as a coupling control device 21,22 is assigned to each coil half-core 17, 18. The transmission of dataoccurs via the data modulation devices 19, 20 and the coupling controldevices 21, 22 are used for the control of the various data modulationdevices 12, 19, 20 as well as alternating voltage measurement device 14with voltage shunt regulator 15. Furthermore, the coupling controldevices 21, 22 are used for the interchange of data, for example, withthe alternating voltage measurement device 14 with voltage shuntregulator 15 and, for example, with a subsea electronic module 29. Thiselectronic module contains the appropriate electronics for controllingthe various items of equipment below sea level and in particular on thesea bed, such as valves, blow-out preventers, actuators and similarequipment. Generally, the appropriate electronics is containedredundantly in the electronic module.

In the following the functioning principle of the control and supplysystem 1 according to the invention is briefly described basedespecially on FIG. 2.

According to the invention, supply of the control and actuation device 6occurs with direct voltage through the subsea cable 5. Here, the directvoltage is converted to alternating voltage by an appropriate DC/ACconverter 8 only when it reaches the end of the long subsea cable. Abovethe surface of the sea a three-phase alternating voltage is converted byan AC/DC converter to, for example, an output voltage from 3000 to 6000V. The voltage value depends on the power requirements of the system.

Then, the stable and filtered direct voltage is passed to coaxialconductors in the subsea cable, whereby first data signals are modulatedonto the voltage via a suitable data modulation device such as a modemor similar device.

Since coaxial conductors exhibit optimum properties with regard toattenuation and electrical noise, high data transmission rates of atleast 100 to 600 kBaud are possible using such conductors.

On the sea bed or below the surface of the sea a demodulation of thedata signals occurs using a suitable data modulation device, again suchas a modem. Then, conversion of the voltage occurs by a DC/AC converterinto, for example, a rectangular wave voltage of 300 V with a frequencyof 20 kHz. This alternating voltage can be transmitted over normalconnection equipment to the various electrical devices. Only slightfiltering is required without large electrolytic capacitors. Thetransformer 16 used for the conversion of the alternating voltage of theDC/AC converter to the appropriate voltage values comprises two coilhalf-cores 18, 19, which are separated by an air gap. The coilhalf-cores are assigned to one another, separable from one another andare formed mutually symmetrically. This transformer provides theinductive coupling.

Then follows a measurement of the amplitude of the rectangular wavevoltage by the alternating voltage measurement device 14, to whichfurthermore a voltage shunt regulator 15 is assigned. A static anddynamic stabilization of the output voltage is largely provided by thesetwo devices in the transformer output. Appropriate losses from thetransformer and other devices in the control and actuation device 6 canbe dissipated directly through contact to the sea water via appropriatewall construction on the device.

Data transmission from the measurement device 14 via the data modulationdevice 20 and 19 and via the further data modulation device 12 and backto the voltage supply and control device 3 is possible for regulation ofthe voltage supply.

Using appropriate calculations for the required voltage values andpowers, a conductor cross-sectional area of only approximately 2 mm 2arises for, for example, a length of 50 km of subsea cable with thevoltage control and supply system according to the invention. This is asubstantially lower cross-sectional area than with systems known inpractice, see FIGS. 1(a) and (b).

In addition, high data transmission rates are possible due to the simplemodulation and demodulation with respect to the direct voltage and thecoaxial cable used. Through the devices used in the system according tothe invention a stable supply voltage and high system reliability arise.

1. A control and supply system for subsea electrical devices comprising:at least one voltage supply and control device above sea level; a subseacable connecting said voltage supply and control device with theelectrical devices; a control and actuating device arranged in situ withthe electrical devices; a connecting line connecting said control andactuating device to the electrical devices; wherein said voltage supplyand control device comprises at least one AC/DC converter and is adaptedto produce a first direct voltage that is fed into said subsea cable;and wherein the control and actuating device comprises at least oneDC/DC or DC/AC converter for converting the direct voltage transmittedby said subsea cable into a second voltage such that the second voltagecan be transmitted to the electrical devices via said connecting line.2. The control and supply system according to claim 1, furthercomprising an alternating voltage source connected to the voltage supplyand control device and adapted to supply a three-phase alternatingvoltage.
 3. The control and supply system according to claim 1, whereinsaid voltage supply and control device and said control and actuationdevice each comprise at least one data modulation device.
 4. The controland supply system according to claim 3, wherein the data modulationdevice of said voltage supply and control device is positioned after theAC/DC converter.
 5. The control and supply system according to claim 3,wherein said voltage supply and control device is connected to anexternal data transmission device.
 6. The control and supply systemaccording to claim 3, wherein the data modulation device of said controland actuation device is positioned after the DC/DC or DC/AC converter.7. The control and supply system according to claim 1, furthercomprising an overcurrent control device assigned to the DC/DC or DC/ACconverter.
 8. The control and supply system according to claim 1,wherein the DC/AC converter is inductively coupled with an alternatingvoltage measurement device or a voltage shunt regulator.
 9. The controland supply system according to claim 8, further comprising a transformerinductively coupled between the DC/AC converter and the alternatingvoltage measurement device.
 10. The control and supply system accordingto claim 9, wherein the transformer comprises two separable coilhalf-cores which are largely symmetrical and assigned to one another.11. The control and supply system according to claim 10, furthercomprising an air gap between the coil half-cores is a maximum of 4 mmand a maximum of 2 mm wide.
 12. The control and supply system accordingto claim 10, further comprising a data modulation device assigned toeach coil half-core.
 13. The control and supply system according toclaim 12, further comprising a coupling control device assigned to eachcoil half-core and adapted to control the data modulation devices of theDC/AC converter and the alternating voltage measurement device.
 14. Thecontrol and supply system according to claim 8, wherein the alternatingvoltage measurement device is connected to the electrical devicesthrough the connecting line.
 15. The control and supply system accordingto claim 14, wherein the second voltage is an alternating voltage havingan amplitude adapted to be measured by the alternating voltagemeasurement device.
 16. The control and supply system according to claim15, wherein the alternating voltage provided by the DC/AC converter is arectangular wave voltage.
 17. The control and supply system according toclaim 15, wherein the alternating voltage is statically and dynamicallystabilized.
 18. The control and supply system according to claim 8,wherein voltage shunt regulator is formed bi-directionally.
 19. Thecontrol and supply system according to claim 1, wherein the transmissionof data along said subsea cable is carried out bi-directionally.
 20. Thecontrol and supply system according to claim 1, wherein said subseacable comprises a separate line for each of the electrical devices. 21.The control and supply system according to claim 1, further comprising amultiplexer device in between said voltage supply and control device andsaid control and actuating device.